LARSE Exp/research

• -research done after Northridge quake
• -seismologists found shaking more intense on alluvium
• -thicker the alluvium in the alluvial basins under/near LA=more intense shaking
• -shaking is usually worse in the middle of the basins

• -Los Angelos Region Seismic Experiment (currently in progress)
• -mapping the subsurface beneath LA and neighboring basins
• -done by underground sound waves
• -Important b/c it is not possible to predict the amount of shaking from future quakes by only examining the ground type at the earth's surface
• -thickness of alluvium affects amount of shaking
• -exp may also tell us why seismic waves are focused in certain areas (ex:santa monica during Northridge quake) causing more damage in these areas
• -this would allow them to predict exactly what areas could expect amplified shaking from different quakes(w/ diff. epicenter locations)

1)the alluvial basin beneath the san gabriel valley is 50% deeper than previously thought. Since thickness of alluvium affects the level of shaking, the quake hazard here is larger than thought.

2) the San Madre and Whittier faults merge, at depth, into what the seismologists have called the "master blind thrust fault". This fault extends to the East towards San Andreas fault. Stress can be transferred along the connected fault system into the LA basin, increasing the quake hazard for LA

• A) unknown faults
• B) quakes can trigger quakes on other faults at great distances
• C) quakes can change stress pattern in the rocks, increases probability of future quakes on neighboring faults
• D)quakes can jump from fault to another
• E) are faults connected at depth, if rupture on fault it could trigger rupture on another fault
• F) Clustering in time and space of quakes
• G)ground type and depth of basin affect the amount of shaking